1. Field of the Invention
The present invention relates to a valve operating system for an internal combustion engine of the type, having air pressure chambers for biasing the engine valves in the closed direction thereof and, in particular, the type having; an air supply passage connected to the air pressure chambers for supplying air thereto and a relief passage connected to the air pressure chambers for releasing air therefrom.
2. Description of the Prior Art
There is a conventionally known valve operating system in which the pressure in an air pressure chamber is varied in accordance with the operational state of the engine, thereby varying the load of the air spring on the valve, as described in, e.g., Japanese Patent Application Laid-open No. 230910/90.
In such a conventional valve operating system, however, air pressure in the air pressure chamber is controlled at the air-supply side where air is supplied to the air pressure chamber. Therefore, due to a difference in the amount of air flowing into each of a plurality of air pressure chambers which are provided corresponding to respective engine valves of cylinders, as well as due to deviation in the amount of air leaking from each of the air pressure chambers, the actual air pressure in each of the air pressure chambers may be deviated from a target value, or a difference in pressure in the air pressure chambers may become large, which hinders the objective of increasing the maximum number of revolutions of the engine. Further, during a transitional stage where the operational state of the engine is changing, the pressure in the air pressure chamber may not be change swiftly and thus the followability of the valve with the cam may be poor.
Further, when the known conventional valve operating system is applied to a multi-cylinder type internal combustion engine, one pressure chamber defining member is secured to the cylinder head with respective to each cylinder and a piston which is operatively connected to the cam shaft common to all the cylinders and which is secured to an engine valve for each cylinder is slidably received in each pressure chamber defining member to define an air chamber between each pressure chamber defining member and the piston. Therefore, passages which should be connected to each of the air pressure chambers are connected to each of the pressure chamber defining members. Thus, the number of parts is increased, the structure becomes complicated, and sealability becomes poor. Moreover, the cam shaft is rotatbly supported by a cam holder which is mounted to the cylinder head between each of the pressure chamber defining members and thus, the construction becomes more complicated.